Rules chairman: We need solid proof

Troy Calhoun is willing to take measures to slow down college offenses, but only if he sees hard evidence that defending an up-tempo offense creates genuine health risks.

Six days after asserting a rule change would be made "to enhance student-athlete safety by guaranteeing a small window for both teams to substitute," the Air Force coach and NCAA Football Rules Committee chairman backtracked in a conference call with reporters, saying he has seen no such data.